ISIL 'key suspect' in Istanbul's Ataturk airport attack

Turkey has declared a day of national mourning after three suicide bombers attacked Istanbul's Ataturk Airport, killing at least 41 people and wounding 239.

The attackers arrived at Ataturk, Europe's third-busiest airport, late on Tuesday evening where they opened fire before blowing themselves up.

The Turkish government ordered flags to be flown at half-mast on Wednesday, as investigators pored over video footage and witness statements.

Turkish officials said that 23 of the dead were Turkish, and 13 were foreign, including five Saudis and two Iraqis. Citizens from China, Jordan, Tunisia, Uzbekistan, Iran and Ukraine were also among the 13 foreigners killed.

The Istanbul governor's office said 109 of the 239 people hospitalised had since been discharged.

Security camera footage shared on social media appeared to capture two of the blasts. In one clip, a huge ball of flame erupts at an entrance to the terminal building, scattering terrified passengers.

Another video shows a black-clad attacker running inside the building before collapsing to the ground - apparently felled by a police bullet - and blowing himself up.

Turkish President Recep Tayyip Erdogan called for a 'joint fight' against terror after the attack [EPA]

President Recep Tayyip Erdogan called for a "joint fight" against terror after the attack.

"If states, as all humanity, fail to join forces and wage a joint fight against terrorist organisations, all the possibilities that we dread in our minds will come true one by one," he said in a statement.

"It is clear that this attack is not aimed at achieving any result but only to create propaganda material against our country using simply the blood and pain of innocent people."

One of the attackers "randomly opened fire" as he walked through the terminal building, shortly before three explosions, a witness told Reuters.

"We came right to international departures and saw the man randomly shooting. He was just firing at anyone coming in front of him. He was wearing all black. His face was not masked. I was 50 metres away from him," said Paul Roos, 77, a South African tourist on his way back to Cape Town with his wife.

"We ducked behind a counter but I stood up and watched him. Two explosions went off shortly after one another. By that time he had stopped shooting," Roos said.

"He turned around and started coming towards us. He was holding his gun inside his jacket. He looked around anxiously to see if anyone was going to stop him and then went down the escalator ... We heard some more gunfire and then another explosion, and then it was over."

Ataturk Airport is one of the busiest ports in the world, serving more than 60 million passengers in 2015.

There has been a string of bombings around Turkey over the past year, some of them blamed on ISIL, others claimed by Kurdish groups.